The polyphenylene sulfide (hereinafter abbreviated as “PPS”) resin is an engineering plastic having excellent heat resistance, flame resistance, chemical resistance, electrical insulation property, moist heat resistance, as well as mechanical strength and dimensional stability. The PPS resin can be molded to various molded products, fibers and films by various molding methods including injection molding and extrusion molding and is practically used in a wide range of fields such as electric and electronic components, mechanical components and automobile components.
The PPS resin, however, has the poorer resistance to tracking breakdown occurring under application of a high voltage to the insulator surface, compared with other engineering plastics such as polyamide resins and polyester resins.
Accordingly, irrespective of the good heat resistance, flame resistance, chemical resistance, electrical insulation property, most heat resistance as well as mechanical strength and dimensional stability of the PPS resin described above, the application of the PPS resin is limited in an environment exposed to a relatively high voltage. It has thus been demanded to improve the tracking resistance of the PPS resin composition.
Some approaches have been proposed to improve the tracking resistance of the PPS resin: one proposed application adds magnesium hydroxide, another polymer and an additive to the PPS resin, in order to improve the tracking resistance.
For example, Patent Document 1 is an application that adds magnesium hydroxide and a polyamide resin to the PPS resin, in order to improve the tracking resistance. Patent Document 2 is an application that describes a composition produced by adding magnesium hydroxide, a polyolefin polymer and/or polyolefin copolymer, silicone and a fluororesin to the PPS resin. Patent Document 3 is an application that describes a composition produced by adding magnesium hydroxide and carnauba wax and/or amide carboxylate wax. Patent Document 4 is an application that describes a PPS resin composition using magnesium hydroxide having a specific primary particle diameter to improve the tracking resistance.
In the resin compositions proposed by the above patent documents, however, a high content of magnesium hydroxide is essential for the sufficiently good tracking resistance. The high content, however, disadvantageously leads to significant deterioration of the mechanical strength of the PPS resin composition. These patent documents describe the primary particle diameter of magnesium hydroxide to be contained, but fail to describe the dispersion state of magnesium hydroxide in the composition or in the molded product. These patent documents also fail to describe the kneading method taking into account the dispersion state. In the general melt kneading method, magnesium hydroxide is likely to cause secondary aggregation of magnesium hydroxide. The secondary aggregation disadvantageously leads to deterioration of the mechanical strength. In Patent Document 1, a specific type of polyamide resin is added to the PPS resin. This polyamide, however, has poor heat resistance at the melt processing temperature of the PPS resin and accordingly causes deterioration of the physical properties of the resulting composition.
Patent Document 5 is an application that describes a resin composition produced by adding a large amount of a polyamide to a polyarylene sulfide (hereinafter abbreviated as “PAS”) resin as the method of improving the racking resistance of the PPS resin without using magnesium hydroxide. In Examples of this application, 80 parts or more of the polyamide resin are added to 100 parts of the PPS resin. Such addition of a polyamide having a high melting point maintains the heat resistance, but deteriorates the intrinsic low gas generation, flame resistance, dimensional stability and low water absorption of the PPS resin.
Patent Document 6 is an application that describes a composition having the improved dispersion state of a polyamide resin in the PPS resin. Decreasing the dispersed particle diameter of the amide resin has the excellent effect on improvement of the toughness. The composition of the polyamide in Patent Document 6, however, cannot provide the PPS resin composition having the high tracking resistance.